Multi-user null data packet (NDP) ranging

ABSTRACT

A first communication device prompts a plurality of second communication devices to transmit, during a contiguous time period reserved for a range measurement exchange, respective first null data packets (NDPs) at respective times. The first communication device receives first NDPs from at least some of the second communication devices during the contiguous time period, and transmits one or more second NDPs to the plurality of second communication devices. The first communication device uses reception of the first NDPs and transmission of the one or more second NDPs to determine respective ranges between the first communication device and respective second communication devices.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication entitled “MULTI-USER NULL DATA PACKET (NDP) RANGING”, havinga serial number of 16/054484, having a filing date of Aug. 3, 2018;which claims the benefit of U.S. provisional application entitled“RANGING WITH NEAR FAR STAs”, having a serial number of 62/542614, andhaving a filling date of Aug. 8, 2017, having common inventors, andhaving a common assignee, all of which is incorporated by reference inits entirety.

FIELD OF TECHNOLOGY

The present disclosure relates generally to wireless communicationsystems, and more particularly to communication exchanges betweenwireless communication devices for measuring distances among thewireless communication devices.

BACKGROUND

Wireless local area networks (WLANs) have evolved rapidly over the pastdecade, and development of WLAN standards such as the Institute forElectrical and Electronics Engineers (IEEE) 802.111 Standard family hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughput, such as throughputs in the tens of Gbps range.

Some mobile communication devices include a WLAN network interface andsatellite positioning technology, such as global positioning system(GPS) technology. GPS technology in mobile communication devices isuseful for navigating to a desired location, for example. However, GPStechnology does not typically provide accurate location information whena GPS receiver is not in direct sight of a GPS satellite, and thus GPStechnology is often not useful for providing location information whilea mobile communication device is within a building such as an airport, ashopping mall, etc., within a tunnel, etc.

Techniques for determining a position of a communication device usingWLAN technology are now under development. For example, a distancebetween a first communication and a second communication device isdetermined by measuring a time of flight of WLAN transmissions betweenthe first communication device and the second communication device, andthe determined distance. Similarly, distances between the firstcommunication device and multiple third communication devices aredetermined. Then, the determined distances are used to estimate alocation of the first communication device by employing, for example, atriangulation technique. For a first communication device havingmultiple antennas, an angle of departure (AoD) of a WLAN transmissioncan be determined. Similarly, for a second communication device havingmultiple antennas, an angle of arrival (AoA) of the WLAN transmissionfrom the first communication device can be determined. The AoD and theAoA, along with the determined distances, can be also be used forestimating the location of the first communication device.

SUMMARY

In an embodiment, a method for performing a ranging measurementprocedure includes: prompting, at a first communication device, aplurality of second communication devices to transmit, during acontiguous time period reserved for a range measurement exchange,respective first null data packets (NDPs) at respective times;receiving, at the first communication device, first NDPs from at least:some of the second communication devices during the contiguous timeperiod; transmitting, by the first communication device, one or moresecond NDPs to the plurality of second communication devices; and using,at the first communication device, reception of the first NDPs andtransmission of the one or more second NDPs to determine respectiveranges between the first communication device and respective secondcommunication devices.

In another embodiment, an apparatus comprises a network interface deviceassociated with a first communication device. The network interfacedevice is implemented on one or more integrated circuit (IC) devices,and is configured to: prompt a plurality of second communication devicesto transmit, during a contiguous time period reserved for a rangemeasurement exchange, respective first null data packets (NDPs) atrespective times, receive first NDPs from at least some of the secondcommunication devices during the contiguous time period, transmit one ormore second NDPs to the plurality of second communication devices, anduse reception of the first NDPs and transmission of the one or moresecond NDPs to determine respective ranges between the firstcommunication device and respective second communication devices.

In yet another embodiment, a method for performing a ranging measurementprocedure includes: receiving, at a first communication device, a packetfrom a second communication device, the packet including informationconfigured to prompt the first communication device to transmit a firstnull data packet (NDP) during a contiguous time period reserved for arange measurement exchange involving the first communication, the secondcommunication device, and one or more other communication devices;responsive to receiving the packet, transmitting, by the firstcommunication device, the first NDP to the second communication deviceduring the contiguous time period; receiving, by the first communicationdevice, a second NDP from the second communication during the contiguoustime period; and using, at the first communication device, transmissionof the first NDP and reception of the second NDP to determine a rangebetween the first communication device and the second communicationdevice.

In still another embodiment, an apparatus comprises: a network interfacedevice associated with a first communication device. The networkinterface device is implemented on one or more integrated circuit (IC)devices, and is configured to: receive a packet from a secondcommunication device, the packet including information configured toprompt the first communication device to transmit a first null datapacket (NDP) during a contiguous time period reserved for a rangemeasurement exchange involving the first communication, the secondcommunication device, and one or more other communication devices,responsive to receiving the packet, transmits the first NDP to thesecond communication device during the contiguous time period, receive asecond NDP from the second communication during the contiguous timeperiod, and use transmission of the first NDP and reception of thesecond NDP to determine a range between the first communication deviceand the second communication device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN), according to an embodiment.

FIG. 2A is a diagram of an example multi-user (MU) ranging measurementexchange in an MU ranging measurement procedure, according to anembodiment.

FIG. 2B is a timing diagram of the example MU ranging measurementexchange of FIG. 2A, according to an embodiment.

FIG. 3 is a diagram of another example MU ranging measurement exchange,according to another embodiment.

FIG. 4 is a diagram of another example MU ranging measurement exchange,according to another embodiment.

FIG. 5 is a diagram of another example MU ranging measurement exchange,according to another embodiment.

FIG. 6 is a diagram of an example MU ranging measurement exchangesimilar to the MU ranging measurement exchange of FIG. 5 , illustratinga scenario in which a null data packet (NDP) is not received as a resultof a collision, according to another embodiment.

FIG. 7 is a flow diagram of an example method for performing a rangingmeasurement procedure, according to an embodiment.

FIG. 8 is a flow diagram of another example method for performing aranging measurement procedure, according to another embodiment.

DETAILED DESCRIPTION

Techniques for performing ranging measurement packet exchanges among agroup of communication devices described below are discussed in thecontext of wireless local area networks (WLANs) that utilize protocolsthe same as or similar to protocols defined by the 802.11 Standard fromthe Institute of Electrical and Electronics Engineers (IEEE) merely forexplanatory purposes. In other embodiments, however, ranging measurementtechniques are utilized in other types of wireless communication systemssuch as personal area networks (PANs), mobile communication networkssuch as cellular networks, metropolitan area networks (MANs), etc.

FIG. 1 is a block diagram of an example WLAN 110, according to anembodiment. The WLAN 110 includes an access point (AP) 114 thatcomprises a host processor 118 coupled to a network interface device122. The network interface 122 includes a medium access control (MAC)processor 126 and a physical layer (PHY) processor 130. The PHYprocessor 130 includes a plurality of transceivers 134, and thetransceivers 134 are coupled to a plurality of antennas 138. Althoughthree transceivers 134 and three antennas 138 are illustrated in FIG. 1, the AP 114 includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 134 and antennas 138 in other embodiments. In someembodiments, the AP 114 includes a higher number of antennas 138 thantransceivers 134, and antenna switching techniques are utilized.

The network interface 122 is implemented using one or more integratecircuits (ICs) configured to operate as discussed below. For example,the MAC processor 126 may be implemented, at least partially, on a firstIC, and the PHY processor 130 may he implemented, at least partially, ona second IC. As another example, at least a portion of the MAC processor126 and at least a portion of the PHY processor 130 may be implementedon a single IC. For instance, the network interface 122 may beimplemented using a system on a chip (SoC), where the SoC includes atleast a portion of the MAC processor 126 and at least a portion of thePHY processor 130.

In an embodiment, the host processor 118 includes a processor configuredto execute machine readable instructions stored in a memory device (notshown) such as a random access memory (RAM), a read-only memory (ROM), aflash memory, etc. In an embodiment, the host processor 118 may beimplemented, at least partially, on a first IC, and the network device122 may be implemented, at least partially, on a second IC. As anotherexample, the host processor 118 and at least a portion of the networkinterface 122 may be implemented on a single IC.

In various embodiments, the MAC processor 126 and/or the PHY processor130 of the AP 114 are configured to generate data units, and processreceived data units, that conform to a WLAN communication protocol suchas a communication protocol conforming to the IEEE 802.11 Standard oranother suitable wireless communication protocol. For example, the MACprocessor 126 may be configured to implement MAC layer functions,including MAC layer functions of the WLAN communication protocol, andthe PHY processor 130 may be configured to implement PHY functions,including PHY functions of the WLAN communication protocol. Forinstance, the MAC processor 126 may be configured to generate MAC layerdata units such as MAC service data units (MSDUs), MAC protocol dataunits (MPDUs), etc., and provide the MAC layer data units to the PHYprocessor 130. The PHY processor 130 may be configured to receive MAClayer data units from the MAC processor 126 and encapsulate the MAClayer data units to generate PHY data units such as PHY protocol dataunits (PPDUs) for transmission via the antennas 138. Similarly, the PHYprocessor 130 may be configured to receive PHY data units that werereceived via the antennas 138, and extract MAC layer data unitsencapsulated within the PHY data units. The PHY processor 130 mayprovide the extracted MAC layer data units to the MAC processor 126,which processes the MAC layer data units.

The PHY processor 130 is configured to downconvert one or more radiofrequency (RF) signals received via the one or more antennas 138 to oneor more baseband analog signals, and convert the analog basebandsignal(s) to one or more digital baseband signals, according to anembodiment. The PHY processor 130 is further configured to process theone or more digital baseband signals to demodulate the one or moredigital baseband signals and to generate a PPDU. The PHY processor 130includes amplifiers (e.g., a low noise amplifier (LNA), a poweramplifier, etc.), a radio frequency (RF) downconverter, an RFupconverter, a plurality of filters, one or more analog-to-digitalconverters (ADCs), one or more digital-to-analog converters (DACs), oneor more discrete Fourier transform (DFT) calculators (e.g., a fastFourier transform (FFT) calculator), one or more inverse discreteFourier transform (IDFT) calculators (e.g., an inverse fast Fouriertransform (IFFT) calculator), one or more modulators, one or moredemodulators, etc.

The PHY processor 130 is configured to generate one or more RF signalsthat are provided to the one or more antennas 138. The PHY processor 130is also configured to receive one or more RF signals from the one ormore antennas 138.

The MAC processor 126 is configured to control the PHY processor 130 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 130, andoptionally providing one or more control signals to the PHY processor130, according to some embodiments. In an embodiment, the MAC processor126 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a readROM, a flash memory, etc. In an embodiment, the MAC processor 126includes a hardware state machine.

The WLAN 1110 includes a plurality of client stations 154. Althoughthree client, stations 154 are illustrated in FIG. 1 , the WLAN 110includes other suitable numbers (e.g., 1, 2, 4, 5, 6, etc.) of clientstations 154 in various embodiments. The client station 154-1 includes ahost processor 158 coupled to a network interface device 162. Thenetwork interface 162 includes a MAC processor 166 and a PHY processor170. The PHY processor 170 includes a plurality of transceivers 174, andthe transceivers 174 are coupled to a plurality of antennas 178.Although three transceivers 174 and three antennas 178 are illustratedin FIG. 1 , the client station 154-1 includes other suitable numbers(e.g., 1, 2, 4, 5, etc.) of transceivers 174 and antennas 178 in otherembodiments. In some embodiments, the client station 154-1 includes ahigher number of antennas 178 than transceivers 174, and antennaswitching techniques are utilized.

The network interface 162 is implemented using one or more ICsconfigured to operate as discussed below. For example, the MAC processor166 may be implemented on at least a first IC, and the PHY processor 170may be implemented on at least a second IC. As another example, at leasta portion of the MAC processor 166 and at least a portion of the PHYprocessor 170 may be implemented on a single IC. For instance, thenetwork interface 162 may be implemented using an SoC, where the SoCincludes at least a portion of the MAC processor 166 and at least aportion of the PHY processor 170.

In an embodiment, the host processor 158 includes a processor configuredto execute machine readable instructions stored in a memory device (notshown) such as a RAM, a ROM, a flash memory, etc. In an embodiment, thehost processor 158 may be implemented, at least partially, on a firstIC, and the network device 162 may be implemented, at least partially,on a second IC. As another example, the host processor 158 and at leasta portion of the network interface 162 may be implemented on a singleIC.

In various embodiments, the MAC processor 166 and the PHY processor 170of the client device 154-1 are configured to generate data units, andprocess received data units, that conform to the WLAN communicationprotocol or another suitable communication protocol. For example, theMAC processor 166 may be configured to implement MAC layer functions,including MAC layer functions of the WLAN communication protocol, andthe PHY processor 170 may be configured to implement PHY functions,including PHY functions of the WLAN communication protocol. The MACprocessor 166 may be configured to generate MAC layer data units such asMSDUs, MPDUs, etc., and provide the MAC layer data units to the PHYprocessor 170. The PHY processor 170 may be configured to receive MAClayer data units from the MAC processor 166 and encapsulate the MAClayer data units to generate PHY data units such as PPDUs fortransmission via the antennas 178. Similarly, the PHY processor 170 maybe configured to receive PHY data units that were received via theantennas 178, and extract MAC layer data units encapsulated within thePHY data units. The PHY processor 170 may provide the extracted MAClayer data units to the MAC processor 166, which processes the MAC layerdata units.

The PHY processor 170 is configured to downconvert one or more RFsignals received via the one or more antennas 178 to one or morebaseband analog signals, and convert the analog baseband signal(s) toone or more digital baseband signals, according to an embodiment. ThePHY processor 170 is further configured to process the one or moredigital baseband signals to demodulate the one or more digital basebandsignals and to generate a PPDU. The PHY processor 170 includesamplifiers (e.g., an LNA, a power amplifier, etc.), an RF downconverter,an RF upconverter, a plurality of filters, one or more ADCs, one or moreDACs, one or more DFT calculators (e.g., an FFT calculator), one or moreIDFT calculators (e.g., an IFFT calculator), one or more modulators, oneor more demodulators, etc.

The PHY processor 170 is configured to generate one or more RF signalsthat are provided to the one or more antennas 178. The PHY processor 170is also configured to receive one or more RF signals from the one ormore antennas 178.

The MAC processor 166 is configured to control the PHY processor 170 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 170, andoptionally providing one or more control signals to the PHY processor170, according to some embodiments. In an embodiment, the MAC processor166 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a ROM,a flash memory, etc. In an embodiment, the MAC processor 166 includes ahardware state machine.

In an embodiment, each of the client stations 154-2 and 154-3 has astructure that is the same as or similar to the client station 154-1.Each of the client stations 154-2 and 154-3 has the same or a differentnumber of transceivers and antennas. For example, the client station154-2 and/or the client station 154-3 each have only two transceiversand two antennas (not shown), according to an embodiment.

PPDUs are sometimes referred to herein as packets. MPDUs are sometimesreferred to herein as frames.

FIG. 2A is a diagram of an example multi-user (MU) ranging measurementexchange 200 in an MU ranging measurement procedure, according to anembodiment. The diagram 200 is described in the context of the examplenetwork 110 merely for explanatory purposes. In some embodiments,signals illustrated in FIG. 2A are generated by other suitablecommunication devices in other suitable types of wireless networks.

According to an embodiment, an MU ranging measurement exchange, such asthe MU ranging measurement exchange 200, is an exchange of packetsbetween at least three communication devices (e.g., an AP and at leasttwo client stations) during a contiguous time period reserved for rangemeasurement purposes, wherein the exchange of packets includes i) NDPs,and ii) one or more packets related to the transmission of the NDPs(e.g., a packet that prompts transmission of an uplink NDP, a packetthat announces transmission of a subsequent downlink NDP, etc.).

The MU ranging measurement exchange 200 corresponds to an AP-initiatedMU ranging measurement exchange, according to an embodiment. The MUranging measurement exchange 200 includes an uplink (UL) null datapacket (NDP) frame exchange 204, a downlink (DL) NDP transmissionportion 208, a DL feedback frame exchange 210, and an UL feedback frameexchange 212. In an embodiment, the MU ranging measurement exchange 200also includes a station readiness poll, which is not shown in FIG. 2 .In an embodiment, the uplink UL NDP frame exchange 204, the DL NDPtransmission portion 208, the DL feedback frame exchange 210, and the ULfeedback frame exchange 212 occur within a single transmit opportunityperiod (TXOP). In another embodiment, the uplink UL NDP frame exchange204, the DL NDP transmission portion 208, the DL feedback frame exchange210, and the. UL feedback frame exchange 212 do not occur within asingle TXOP. For example, the uplink UL NDP frame exchange 204 and theDL NDP transmission portion 208 occur within a single TXOP, whereas theDL feedback frame exchange 210 and the UL feedback frame exchange 212occur after the single TXOP (e.g., in another TXOP or in multiple otherTXOPs).

In the UL NDP exchange 204, a first communication device (e.g., the AP114) transmits a DL PPDU 216 that includes a trigger frame to cause agroup of multiple second communication devices (e.g., client stations154) to simultaneously transmit, as part of an uplink (UL) MUtransmission 220, UL null data packets (NDPs) 224. In an embodiment, thetrigger frame in the PPDU 216 is a type of trigger frame specificallyfor initiating an MU ranging measurement exchange such as the MU rangingmeasurement exchange 200. The trigger frame in the PPDU 216 causesmultiple client stations 154 to begin simultaneously transmitting the ULMU transmission 220 a defined time period after an end of the PPDU 216.In an embodiment, the defined time period is a short interframe space(SIFS) as defined by the IEEE 802.11 Standard. In other embodiments,another suitable time period is utilized.

In an embodiment, the UL MU transmission 220 includes an UL MU multipleinput, multiple output (MIMO) transmission having two or more UL NDPs224 from multiple client stations 154, e.g., STA1, STA2, STA3, and STA4.The two or more of the UL NDPs 224 are transmitted within a samefrequency band via different spatial streams (e.g., MU-MIMO). In anotherembodiment, the UL MU transmission 220 includes an UL orthogonalfrequency division multiple access (OFDMA) transmission having two ormore UL NDPs 224 from multiple client stations 154, e.g., STA1, STA2,STA3, and STA4, in different respective frequency bandwidth portions. Inyet another embodiment, three or more UL NDP packets 224 transmittedusing a combination of UL MU-MIMO and UL OFDMA, where at least two NDPsare transmitted using MU-MIMO in a same frequency bandwidth portion viadifferent spatial streams, and at least one NDP is transmitted in atleast one other different frequency bandwidth portion. The UL NDPs 224include PHY preambles having one or more short training fields (STFs),one or more long training fields (LTFs) and one or more signal fields,in an embodiment. In an embodiment, each PHY preamble of each UL NDP 224includes i) a legacy portion having a legacy STF (L-STF), a legacy LTF(L-LTF), and a legacy signal field (L-SIG), and ii) a non-legacy portionhaving a high efficiency STF (HE-STF), one or more high efficiency WiFiLTFs (HE-LTFs), and a high efficiency WiFi signal field (HE-SIG). The ULNDPs 224 omit data portions.

When transmitting the UL NDPs 224, each client station 154 records atime t_(1,k) at which the client station 154 began transmitting aparticular portion of the UL NDP 224 (e.g., a first occurring HE-LTF inthe UL NDP 224), where k is an index indicating the particular clientstation 154. Similarly, when the AP 114 receives each UL NDP 224, the AP114 records a time t_(2,k) at which the AP 114 began receiving theparticular portion of the UL NDP 224 (e.g., the first occurring HE-LTFin the UL NDP 224).

In some embodiments, when transmitting the UL NDPs 224, each of at leastsome of the client stations 154 (e.g., client stations 154 with multipleantennas 174) records an angle of departure, AoD_(1,k), at which the ULNDP 224 left the antennas 178 of the client station 154. Similarly, whenthe AP 114 receives each UL NDP 224, the AP 114 records an angle ofarrival, AoA_(1,k), at which the UL NDP 224 arrived at the antennas 138of the AP 114.

FIG. 2B is a timing diagram of the example MU ranging measurementexchange 200 of FIG. 2A. As illustrated in FIG. 2B, each client station154 records the time t_(1,k) at which the client station 154 begantransmitting the particular portion of the UL NDP 224 (e.g., the firstoccurring HE-LTF in the UL NDP 224), and records the AoD_(1,k) at whichthe UL NDP 224 left the antennas 178 of the client station 154.Additionally, the AP 114 records the time t_(2,k) at which the AP 114began receiving the respective particular portion of each UL NDP 224(e.g., the first occurring HE-LTF in the UL NDP 224), and the AoA_(1,k),at which each respective UL NDP 224 arrived at the antennas 138 of theAP 114.

Referring now to FIGS. 2A and 2B, responsive to the UL MU transmission220, the AP 114 begins transmitting a DL PPDU 228 that includes an NDPannouncement (NDPA) frame a defined time period after an end of the ULMU transmission 220. In an embodiment, the defined time period is SIFS.In other embodiments, another suitable time period is utilized. The NDPAframe in the PPDU 228 is configured to cause the client stations 154 tobe prepared to receive an NDP from the AP 114, according to anembodiment.

The AP 114 generates a DL PPDU 232 and begins transmitting the DL PPDU232 a defined time period after an end of the DL PPDU 228. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized. The DL PPDU 232 is a MU PPDUthat includes DL NDPs 236 to respective client stations 154. In anotherembodiment, the AP 1114 transmits a single DL NDP 236 using a SU DLtransmission (e.g., with a broadcast destination address) to the clientstations 154. The DL NDP(s) 236 include PHY preamble(s) having one ormore STFs, one or more LTFs and one or more signal fields, in anembodiment. In an embodiment, the PHY preamble of the DL NDP 236includes i) a legacy portion having an L-STF, an L-LTF, and an L-SIG,and ii) a non-legacy portion having an HE-STF, one or more HE-LTFs, andone or more HE-SIGs. The DL NDP(s) 236 omit data portions. In anembodiment, different DL NDPs 236 are transmitted in different frequencybandwidth portions (e.g., OFDMA). In some embodiments, two or more ofthe DL NDPs 236 are transmitted within a same frequency band (e.g., twoor more of the DL NDPs 236 span the same frequency band) using differentspatial streams (e.g., the two or more DL NDPs 236 are transmitted usingMU-MIMO). In another embodiment, a single DL NDP 236 is broadcast to theclient stations 154.

When transmitting the DL NDP(s) 236, the AP 114 records a time t_(3,k)at which the AP 114 began transmitting a particular portion of the DLNDP 236 (e.g., a first occurring HE-LTF in the DL NDP 236). Similarly,when each client station 154 receives the corresponding DL NDP 236, theclient station 154 records a time t_(4,k) at which the client station154 began receiving the particular portion of the DL NDP 236 (e.g., thefirst occurring HE-LTF in the DL NDP 236). As illustrated in FIG. 2B,the AP 114 records the time t_(3,k) at which the AP 114 begantransmitting the particular portion of the DL NDP 236 (e.g., the firstoccurring HE-LTF in the DL NDP 236), and the client station 154 recordsthe time t_(4,k) at which the client station 154 began receiving theparticular portion of the DL NDP 236 (e.g., the first occurring HE-LTFin the DL NDP 236).

In some embodiments, when transmitting the DL NDP 236, the AP 114records an AoD_(2,k) at which the DL NDP 236 left the antennas 138 ofthe AP 114. Similarly, when the client station 154 receives the DL NDP236, the client station 154 records an AoA_(2,k) at which the DL NDP 236arrived at the antennas 178 of the client station 154.

In some embodiments, the MU ranging measurement exchange 200 omits theDL PPDU 228. For example, the AP 114 begins transmitting the DL PPDU 232a defined time period after an end of the UL MU transmission 220. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized.

The DL FB exchange 210 includes a DL PPDU 240 (which may be a DL OFDMAtransmission or a DL MU-MIMO transmission) having FB frames 244 formultiple client stations 154, e.g., STA1, STA2, STA3, and STA4. The FBframes 244 are illustrated in FIG. 2A as being transmitted in differentfrequency bandwidth portions. In some embodiments, two or more of the FBframes 244 are transmitted within a same frequency band (e.g., two ormore of the FB frames 244 span the same frequency band) using differentspatial streams (e.g., the two or more FB frames 244 are transmittedusing MU-MIMO).

In some embodiments, the DL PPDU 240 is transmitted a defined timeperiod after an end of the DL PPDU 232. In an embodiment, the definedtime period is SIFS. In other embodiments, another suitable time periodis utilized. In other embodiments, the DL PPDU 240 is transmitted aftersome delay. As discussed above, in some embodiments, the DL PPDU 240 isnot transmitted within a same TXOP as the DL PPDU 232.

The FB frames 244 respectively include the recorded times t_(2,k) andt_(3,k). In some embodiments, each of one or more FB frames 244respectively includes the recorded angles AoA_(1,k) and AoD_(2,k). Insome embodiments, the FB frames 244 optionally also include respectivechannel estimate information determined by the AP 114 based on receptionof the UL NDPs 224.

After receipt of the FB frames 244, one or more of the client stations154 respectively calculate one or more respective of times-of-flightbetween the AP 114 and the one or more client stations 154 using therecorded times t_(1,k), t_(2,k), t_(3,k), and t_(4,k), according to anembodiment. Any suitable technique, including currently knowntechniques, may be utilized to calculate a time-of-flight using therecorded times t_(1,k), t_(2,k), t_(3,k), and t_(4,k). Respectivedistances between the AP 114 and the client stations 154 may becalculated using the calculated times-of-flight, e.g., by respectivelymultiplying the times-of-flight by the speed of light, according to anembodiment.

In some embodiments, one or more of the client stations 154 calculatesestimated positions of one or more of the client stations using thecalculated times-of-flight. For example, the client station 154-1 usestriangulation techniques to calculate an estimated positions of theclient station 154-1 using the calculated time-of-flight, in someembodiments, the client station 154-1 calculates an estimated positionof the client station also using the recorded angles AoD_(1,k),AoA_(1,k), AoD_(2,k), and AoA_(2,k). For example, the recorded anglesAoD_(1,k), AoA_(1,k), AoD_(2,k), and AoA_(2,k) are used as part of atriangulation algorithm for determining a position of the client station154-1.

Responsive to receipt of the FB frames 244, the client stations 154generate an UL MU transmission 250 (which may be an UL OFDMAtransmission or an UL MU MIMO transmission) that includes respective ACKframes 254 from respective client stations, according to an embodiment.The client stations 154 transmit as part of the UL MU transmission 250 adefined time period after an end of the DL transmission 240. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized. The ACK frames 254 areillustrated in FIG. 2A as being transmitted in different frequencybandwidth portions. In some embodiments, two or more of the ACK frames254 are transmitted within a same frequency band (e.g., two or more ofthe ACK frames 254 span the same frequency band) using different spatialstreams (e.g., the two or more ACK frames 254 are transmitted usingMU-MIMO). In some embodiments, the client stations 154 do not transmitthe UL MU transmission 250 in order to reduce a duration of the MUranging measurement exchange 200 and improve efficiency.

In an embodiment, the AP 114 transmits a DL PPDU 260 a defined timeperiod after an end of the UL MU transmission 250. In an embodiment, thedefined time period is SIFS. In other embodiments, another suitable timeperiod is utilized. The PPDU 260 includes a trigger frame to cause thegroup of client stations 154 to simultaneously transmit, as part of anUL MU transmission 264, uplink PPDUs 268 that include rangingmeasurement feedback. The trigger frame in the PPDU 260 causes multipleclient stations 154 to begin simultaneously transmitting the UL MUtransmission 264 a defined time period after an end of the PPDU 260. Inan embodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized.

The UL MU transmission 264 (which may be an UL OFDMA transmission or anUL MU-MIMO transmission) includes UL PPDUs 268 from multiple clientstations 154, e.g., STA1, STA2, STA3, and STA4. The UL PPDUs 268 areillustrated in FIG. 2A as being transmitted in different frequencybandwidth portions. In some embodiments, two or more of the UL PPDUs 268are transmitted within a same frequency band (e.g., two or more of theUL PPDUs 268 span the same frequency band) using different spatialstreams (e.g., the two or more UL PPDUs 268 are transmitted usingMU-MIMO).

The UL PPDUs 268 correspond to uplink ranging measurement feedbackpackets. The PPDUs 268 respectively include the recorded times t_(1,k)and t_(4,k). In some embodiments, each of one or more PPDUs 268respectively includes the recorded angles AoD_(1,k) and AoA_(2,k). Insome embodiments, the PPDUs 268 optionally also include respectivechannel estimate information determined by the client station 154 basedon reception of the DL NDP 236.

After receipt of the PPDUs 268, the AP 114 calculates respective oftimes-of-flight between the AP 114 and the client stations 154 using therecorded times t_(1,k), t_(2,k), t_(3,k), and t_(4,k), according to anembodiment. Any suitable technique, including currently knowntechniques, may he utilized to calculate a time-of-flight using therecorded times t_(1,k), t_(2,k), t_(3,k), and t_(4,k). Respectivedistances between the AP 114 and the client stations 154 may becalculated using the calculated times-of-flight, e.g., by respectivelymultiplying the times-of-flight by the speed of light, according to anembodiment.

In some embodiments, the AP 114 calculates estimated positions of one ormore of the client stations using the calculated times-of-flight. Forexample, the AP 114 uses triangulation techniques to calculate estimatedpositions of one or more of the client stations using the calculatedtimes-of-flight. In some embodiments, the AP 114 calculates estimatedpositions of one or more of the client stations also using the recordedangles AoD_(1,k), AoA_(1,k), AoD_(2,k), and AoA_(2,k). For example, therecorded angles AoD_(1,k), AoA_(1,k), AoD_(1,k), and AoA_(2,k) are usedas part of a triangulation algorithm for determining positions ofcommunication devices.

In another embodiment, the order, in time, of the DL FB exchange 210 andthe UL FB exchange 212 is reversed, and the UL FB exchange 212 occursbefore the DL FB exchange 210. In some embodiments, the DL FB exchange210 is omitted. In some embodiments, the UL FB exchange 212 is omitted.

If a first client station 154 is significantly further away from the AP114 than a second client station 154, a received power (as seen at theAP 114) of a first UL NDP 224 (part of the UL MU transmission 220) fromthe first client station may be significantly lower than a receivedpower (as seen at the AP 114) of a second UL NDP 224 (part of the UL MUtransmission 220) from the second client station, at least in somescenarios (sometimes referred to as a “near-far effect”). Such anear-far effect may adversely affect a ToA estimation(s) by the AP 114of the first UL NDP 224 and/or the second UL NDP 224, e.g., because ofinter-station interference caused by the near--far effect. Additionally,in some embodiments, client stations and APs belong to differentclasses, e.g., Class A and Class B, where different classes havedifferent transmit power accuracy and RSSI estimation accuracy. Whenclient stations of different classes participate in the UL MUtransmission 220, ToA estimations) by the AP 114 of the first UL NDP 224and/or the second UL NDP 224 may be adversely affected.

To address situations in which the near-far effect may degrade ToAestimation(s) by the AP 114 in connection with the UL MU transmission220, several embodiments of MU ranging measurement exchanges that employUL NDPs transmitted at different times are discussed below. The severalembodiments of MU ranging measurement exchanges that employ UL NDPstransmitted at different times discussed below are also useful foravoiding or reducing situations in which STAs with different classes inone MU transmission may degrade ToA estimation(s) by the AP 114 (e.g.,in connection with the UL MU transmission 220).

FIG. 3 is a diagram of a portion 300 of another example MU rangingmeasurement exchange in an MU ranging measurement procedure, accordingto another embodiment. FIG. 3 is described in the context of the examplenetwork 110 merely for explanatory purposes. In some embodiments,signals illustrated in FIG. 3 are generated by other suitablecommunication devices in other suitable types of wireless networks.

The portion 300 of the MU ranging measurement exchange corresponds to anAP-initiated MU ranging measurement exchange (referred to herein as “theMU ranging measurement exchange 300” for ease of reference), accordingto an embodiment. The MU ranging measurement exchange 300 also includesa station readiness poll portion and a feedback exchange portion, whichare not shown in FIG. 3 . For example, the MU ranging measurementexchange 300 also includes a DL FB exchange (e.g., the DL FB exchange210 or another suitable DL FB exchange), and/or are UL FB exchange(e.g., the DL FB exchange 210 or another suitable DL FB exchange), bothof which are not shown in FIG. 3 .

The MU ranging measurement exchange 300 includes the DL PPDU 228 and theDL PPDU 232 discussed with reference to FIG. 2A. The DL PPDU 228 and theDL PPDU 232 are not discussed in detail again for purposes of brevity.

The MU ranging measurement exchange 300 includes an UL NDP frameexchange 304, and a DL NDP transmission portion 308. In an embodiment,the uplink UL NDP frame exchange 304 and the DL NDP transmission portion308 occur within a single TXOP.

In the UL NDP exchange 304, an AP (e.g., the AP 114) transmits multipleDL PPDUs 312 that include respective trigger frames to cause a group ofmultiple client stations 154 (e.g., STA1, STA2, STA3, STA4) to transmitmultiple UL NDPs 316. In an embodiment, the trigger frames in the PPDUs312 are a type of trigger frame specifically for prompting a clientstation to transmit UL NDP as part of a MU ranging measurement exchange.The respective trigger frame in the respective PPDU 312 causes therespective client station 154 to begin transmitting the respective ULNDP 316 a defined time period after an end of the PPDU 312. In anembodiment, the defined time period is SIRS as defined by the IEEE802.11 Standard. In other embodiments, another suitable time period isutilized. In an embodiment, the AP 114 transmits a subsequent PPDU 312 adefined time period after an end of reception of the previous PPDU 312.In an embodiment, the defined time period is SIFS as defined by the IEEE802.11 Standard. In other embodiments, another suitable time period isutilized.

Although FIG. 3 illustrates only one client station transmitting inresponse to each trigger frame 312, in other embodiments a respectiveset of multiple client stations transmit in UL MU transmission(s) inresponse to each of one or more of the trigger frames 312. In anembodiment, the AP 114 selects a set of multiple client stations totransmit NDPs 316 in response to a single trigger frame 312 such thatthe receive power of the multiple NPDs 3116 at the AP 114 is within asuitable range. The AP 114 prompts client stations corresponding tosignificantly different receive power at the AP 114 (e.g., not withinthe suitable range) to transmit NDPs 316 at different times withdifferent trigger frames 312.

The multiple UL NDPs 316 are transmitted within a same frequency band.In another embodiment, at least two UL NDPs 316 are transmitted indifferent respective frequency bandwidth portions. The UL NDPs 3116include PHY preambles having one or more STFs, one or more LTFs, and oneor more signal fields, in an embodiment. In an embodiment, each UL NDP316 includes i) a legacy portion having an L-STF, an L-LTF, and anL-SIG, and ii) a non-legacy portion having an HE-STF, one or moreHE-LTFs, and an HE-SIG. The UL NDPs 316 omit data portions.

When a client station 154 transmits the UL NDP 316, the client station154 records a time t_(1,k) at which the client station 154 begantransmitting a particular portion of the UL NDP 316 (e.g., a firstoccurring HE-LTF in the UL NDP 316), where k is an index indicating theparticular client station 154. Similarly, when the AP 114 receives eachUL NDP 316, the AP 114 records a time at which the AP 114 beganreceiving the particular portion of the UL NDP 316 (e.g., the firstoccurring HE-LTF in the UL NDP 316).

In some embodiments, when the client station 154 transmits the UL NDP316, the client station 154 records an angle of departure, AoD_(1,k), atwhich the UL NDP 316 left the antennas 178 of the client station 154.Similarly, when the AP 114 receives the UL NDP 316, the AP 114 recordsan angle of arrival, AoA_(1,k), at which the UL NDP 316 arrived at theantennas 138 of the AP 114, according to an embodiment.

Because the transmission of the UL NDPs 316 corresponding tosignificantly different receive power (e.g., not within a suitablerange) at the AP 114 do not overlap in time and are received at the AP114 at different times, degradation of ToA estimation(s) by the AP 114caused by the near-far effect (discussed with reference to FIG. 2A) isavoided. For example, the AP 114 prompts client stations of differentclasses to transmit NPDs 316 at different times, in an embodiment. Asanother example, the AP 114 groups client stations 154 according todistance from the AP 114, and prompts client stations of atsignificantly different distances to transmit NPDs 316 at differenttimes, in an embodiment.

In an embodiment, responsive to receiving a last UL NDP 316 (e.g., theUL NDP 316-4), the AP 114 begins transmitting the DL PPDU 228 thatincludes the NDPA frame a defined time period after an end of the lastUL NDP 316 (e.g., the UL NDP 316-4). In an embodiment, the defined timeperiod is SIFS. In other embodiments, another suitable time period isutilized. For example, the AP 114 begins transmitting the DL PPDU 228after a point coordination function interframe space (PIFS) as definedby the IEEE 802.11 Standard, which is longer than SIFS, according to anembodiment. As another example, if the AP 114 does not receive an NDP316 after SIFS, PIFS, or another suitable time period, the AP 114performs a backoff procedure prior to transmitting the DL PPDU 228.

The AP 114 generates the DL PPDU 232 and begins transmitting the DL PPDU232 a defined time period after an end of the DL PPDU 228. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized.

FIG. 4 is a diagram of a portion 400 of another example MU rangingmeasurement exchange in an MU ranging measurement procedure, accordingto another embodiment. FIG. 4 is described in the context of the examplenetwork 110 merely for explanatory purposes. In some embodiments,signals illustrated in FIG. 4 are generated by other suitablecommunication devices in other suitable types of wireless networks.

The portion 400 of the MU ranging measurement exchange corresponds to anAP-initiated MU ranging measurement exchange (referred to herein as “theMU ranging measurement exchange 400” for ease of reference), accordingto an embodiment. The MU ranging measurement exchange 400 also includesa station readiness polling portion and a feedback exchange portion,which are not shown in FIG. 4 . For example, the MU ranging measurementexchange 400 also includes a DL FB exchange (e.g., the DL FB exchange210 or another suitable DL FB exchange), and/or an UL FB exchange (e.g.,the DL FB exchange 210 or another suitable DL FB exchange), both ofwhich are not shown in FIG. 4 .

The MU ranging measurement exchange 400 includes a plurality of DL NDPtransmission portions 404, and a plurality of UL NDP transmissionportions 408. In an embodiment, the plurality of DL NDP transmissionportions 404, and the plurality of UL NDP transmission portions 408occur within a single TXOP.

The AP 114 generates DL PPDUs 412, and during each DL NDP transmissionportion 404, the AP 114 transmits the respective DL PPDU 412 thatincludes an NDPA frame. The DL PPDU 412 is an SU transmission to arespective client station 154, according to an embodiment. The NDPAframe in the PPDU 412 is configured to cause the respective clientstation 154 to be prepared to receive a respective NDP from the AP 114,according to an embodiment.

The AP 114 generates DL NDPs 416, and during each DL NDP transmissionportion 404, the AP 114 transmits the respective DL NDP 416. In anembodiment, the AP begins transmitting the respective DL NDP 416 adefined time period after an end of the respective DL PPDU 412. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized. Each DL NDP 416 is an SUtransmission to a respective client station 154. Each DL NDP 416includes a PHY preamble having one or more STFs, one or more LTFs andone or more signal fields, in an embodiment. In an embodiment, each DLNDP 416 includes i) a legacy portion having an L-STF, an L-LTF, and anL-SIG, and ii) a non-legacy portion having an HE-STF, one or moreHE-LTFs, and one or more HE-SIGs. Each DL NDP 416 omits a data portion.

When transmitting each DL NDP 416, the AP 114 records a time t_(3,k) atwhich the AP 114 began transmitting a particular portion of the DL NDP416 (e.g., a first occurring HE-LTF in the DL NDP 416). Similarly, wheneach client station 154 receives the corresponding DL NDP 416, theclient station 154 records a time t_(4,k) at which the client station154 began receiving the particular portion of the DL NDP 416 (e.g., thefirst occurring HE-LTF in the DL NDP 236).

In some embodiments, when transmitting the DL NDP 416, the AP 114records an AoD_(2,k) at which the DL NDP 416 left the antennas 138 ofthe AP 114. Similarly, when the client station 154 receives the DL NDP416, the client station 154 records an AoA_(2,k) at which the DL NDP 416arrived at the antennas 178 of the client station 154.

In each UL NDP transmission portion 408, the respective client station154 transmits a respective UL NDP 420. In an embodiment, each clientstation 154 is configured to transmit the respective UL NDP 420 inresponse to receiving the respective DL NDP 416. In an embodiment, eachclient station 154 is configured to transmit the respective UL NDP 420 adefined time period after an end of the respective DL NDP 416. In anembodiment, the defined time period is SIPS as defined by the IEEE802.11 Standard. In other embodiments, another suitable time period isutilized.

In a DL NDP transmission portion 404 that follows an UL NDP transmissionportion 408, the AP 114 transmits the respective PPDU 412 a defined timeperiod after an end of reception of the previous UL NPD 420. In anembodiment, the defined time period is SIFS as defined by the IEEE802.11 Standard. In other embodiments, another suitable time period isutilized.

The multiple UL NDPs 420 are transmitted within a same frequency band.In another embodiment, at least two UL NDPs 420 are transmitted indifferent respective frequency bandwidth portions. The UL NDPs 420include PHY preambles having one or more STFs, one or more LTFs, and oneor more signal fields, in an embodiment. In an embodiment, each UL NDP420 includes i) a legacy portion having an L-STF, an L-LTF, and anL-SIG, and ii) a non-legacy portion having an HE-STF, one or moreHE-LTFs, and an HE-SIG. The UL NDPs 420 omit data portions.

When a client station 154 transmits the UL NDP 420, the client station154 records a time t_(1,k) at which the client station 154 begantransmitting a particular portion of the UL NDP 420 (e.g., a firstoccurring HE-LTF in the UL NDP 420), where k is an index indicating theparticular client station 154. Similarly, when the AP 114 receives eachUL NDP 420, the AP 114 records a time t_(2,k) at which the AP 114 beganreceiving the particular portion of the UL NDP 420 (e.g., the firstoccurring HE-LTF in the UL NDP 420).

In some embodiments, when the client station 154 transmits the UL NDP420, the client station 154 records an angle of departure, AoD_(1,k), atwhich the UL NDP 420 left the antennas 178 of the client station 154.Similarly, when the AP 114 receives the UL NDP 420, the AP 114 recordsan angle of arrival, AoA_(1,k), at which the UL NDP 420 arrived at theantennas 138 of the AP 114, according to an embodiment.

Because the transmission of the UL NDPs 420 do not overlap in time andare received at the AP 114 at different times, degradation of ToAestimation(s) by the AP 114 caused by the near-far effect (discussedwith reference to FIG. 2A) is avoided.

FIG. 5 is a diagram of a portion 500 of another example MU rangingmeasurement exchange in an MU ranging measurement procedure, accordingto another embodiment. FIG. 5 is described in the context of the examplenetwork 110 merely for explanatory purposes. In some embodiments,signals illustrated in FIG. 5 are generated by other suitablecommunication devices in other suitable types of wireless networks.

The portion 500 of the MU ranging measurement exchange corresponds to anAP-initiated MU ranging measurement exchange (referred to herein as “theMU ranging measurement exchange 500” for ease of reference), accordingto an embodiment. The MU ranging measurement exchange 500 also includesa station readiness polling portion, a feedback exchange portion, whichis not shown in FIG. 5 . For example, the MU ranging measurementexchange 500 also includes a DL FB exchange (e.g., the DL FB exchange210 or another suitable DL FB exchange), and/or an UL FB exchange (e.g.,the DL FB exchange 210 or another suitable DL FB exchange), both ofwhich are not shown in FIG. 5 .

The MU ranging measurement exchange 500 includes the DL PPDU 228 and theDL PPDU 232 discussed with reference to FIG. 2A. The DL PPDU 228 and theDL PPDU 232 are not discussed in detail again for purposes of brevity.

The MU ranging measurement exchange 500 includes an UL NDP frameexchange 504, and a DL NDP transmission portion 508. In an embodiment,the uplink UL NDP frame exchange 504 and the DL NDP transmission portion508 occur within a single TXOP.

In the UL NDP exchange 504, an AP (e.g., the AP 114) transmits a DL PPDU512 that includes a trigger frame configured to cause a group ofmultiple client stations 154 (e.g., STA1, STA2, STA3, STA4) to transmitmultiple UL NDPs 516. In an embodiment, the trigger frame in the PPDU512 is a type of trigger frame specifically for prompting a clientstation to transmit an UL NDP as part of a MU ranging measurementexchange.

The trigger frame in the PPDU 512 includes information indicating anorder, in time, in which client stations 154 in the group are totransmit UL NDPs 516, according to an embodiment. The trigger frame inthe PPDU 512 is configured to prompt a first client station 154 (e.g.,STA1) to begin transmitting the UL NDP 516-1 a defined time period afteran end of the PPDU 512. In an embodiment, the defined time period isSIRS as defined by the IEEE 802.11 Standard. In other embodiments,another suitable time period is utilized.

Each remaining client station 154 in the group is configured to begintransmitting the respective UL NDP 516 a defined time period after anend of the previously transmitted UL NDP 516. In an embodiment, thedefined time period is SIFS as defined by the IEEE 802.11 Standard. Inother embodiments, another suitable time period is utilized.

The multiple UL NDPs 516 are transmitted within a same frequency band.In another embodiment, at least two UL NDPs 516 are transmitted indifferent respective frequency bandwidth portions. The UL NDPs 516include PHY preambles having one or more STFs, one or more LTFs, and oneor more signal fields, in an embodiment. In an embodiment, each UL NDP516 includes i) a legacy portion having an L-STF, L-LTF, and an L-SIG,and ii) a non-legacy portion having an HE-STF, one or more HE-LTFs, andan HE-SIG. The UL NDPs 516 omit data portions.

Although FIG. 5 illustrates only one client station 154 transmitting ata time, in other embodiments a respective set of multiple clientstations transmit NDPs 516 in UL MU transmission(s). In an embodiment,the AP 114 selects a set of multiple client stations to transmit NDPs516 simultaneously such that the receive power of the multiple NPDs 516at the AP 114 is within a suitable range. The AP 114 prompts clientstations corresponding to significantly different receive power at theAP 114 (e.g., not within the suitable range) to transmit NDPs 516 atdifferent times.

When a client station 154 transmits the UL NDP 516, the client station154 records a time t_(1,k) at which the client station 154 begantransmitting a particular portion of the UL NDP 516 (e.g., a firstoccurring HE-LTF in the UL NDP 316), where k is an index indicating theparticular client station 154. Similarly, when the AP 114 receives eachUL NDP 516, the AP 114 records a time t_(2,k) at which the AP 114 beganreceiving the particular portion of the UL NDP 516 (e.g., the firstoccurring HE-LTF in the UL NDP 316).

In some embodiments, when the client station 154 transmits the UL NDP516, the client station 154 records an angle of departure, AoD_(1,k), atwhich the UL NDP 516 left the antennas 178 of the client station 1154.Similarly, when the AP 114 receives the UL NDP 516, the AP 114 recordsan angle of arrival, AoA_(1,k), at which the UL NDP 516 arrived at theantennas 138 of the AP 114, according to an embodiment.

Because the transmission of the UL NDPs 516 corresponding tosignificantly different receive power (e.g., not within a suitablerange) at the AP 114 do not overlap in time and are received at the AP114 at different times, degradation of ToA estimation(s) by the AP 114caused by the near-far effect (discussed with reference to FIG. 2A) isavoided. For example, the AP 114 prompts client stations of differentclasses to transmit NPDs 516 at different times, in an embodiment. Asanother example, the AP 114 groups client stations 154 according todistance from the AP 114, and prompts client stations of atsignificantly different distances to transmit NPDs 516 at differenttimes, in an embodiment.

In an embodiment, responsive to receiving a last UL NDP(s) 516 (e.g.,the UL NDP 516-4), the AP 114 begins transmitting the DL PPDU 228 thatincludes the NDPA frame a defined time period after an end of the lastUL NDP 516 (e.g., the UL NDP 516-4). In an embodiment, the defined timeperiod is SIFS. In other embodiments, another suitable time period isutilized. For example, the AP 114 begins transmitting the DL PPDU 228after PIFS, according to an embodiment. As another example, if the AP114 does not receive the last UL NDP(s) 516 after SIFS, PIFS, or anothersuitable time period, the AP 114 performs a backoff procedure prior totransmitting the DL PPDU 228.

The AP 114 generates the DL PPDU 232 and begins transmitting the DL PPDU232 a defined time period after an end of the DL PPDU 228. In anembodiment, the defined time period is SIFS. In other embodiments,another suitable time period is utilized.

In some situations, a client station 154 may not correctly receive theDL PPDU 512 (which includes the trigger frame), and thus the clientstation 154 does not transmit the respective UL NDP 516, FIG. 6 is adiagram of the example MU ranging measurement exchange 500 of FIG. 5 ,but in which STA2 does not receive the DL PPDU 512 (which includes thetrigger frame) because of a collision 604.

The AP 114 waits a suitable time period after receiving the UL NDP 516-1to begin receiving the UL NDP 516-2 from STA2. In an embodiment, thesuitable time period is PIFS. In another embodiment, the time period isanother suitable time period other than PIFS.

In the scenario, the AP 114 does not begin receiving the UL NDP 516-2from STA2 within the suitable time period. As a result, the AP 114generates a DL PPDU 604 having another trigger frame 604 and transmitsthe DL PPDU 604. The trigger frame in the DL PPDU 604 is configured toprompt the remaining client stations 154 (e.g., STA3 and STA4) totransmit their respective UL NDPs 516.

In an embodiment, the AP 114 is configured to generate and transmit theDL PPDU 604 such that the DL PPDU 604 ends at approximately a time atwhich the UL NDP 516-2 from STA2 would have ended if STA2 hadtransmitted the UL NDP 516-2. As a result, the times at which the UL NDP516-3 and the UL NDP 516-4 are transmitted is the approximately the sameas the times at which the UL NDP 516-3 and the UL NDP 516-4 would havebeen transmitted if STA2 had transmitted the UL NDP 516-2. In anembodiment, the AP 114 uses a first modulation and coding scheme (MCS)when transmitting the DL PPDU 604 which is different than a second MCSthe AP 114 used when transmitting the DL PPDU 512. In an embodiment, theAP 114 chooses the first MCS from among a plurality of MCSs to adjust aduration of the DL PPDU 604 in an attempt to make an end of thetransmission of the DL PPDU 604 occur at approximately a time at whichthe UL NDP 516-2 from STA2 would have ended if STA2 had transmitted theUL NDP 516-2. In an embodiment, the AP 114 adds padding (e.g., PHYpadding and/or MAC padding) to a data portion of the DL PPDU 604 toadjust a duration of the DL PPDU 604 in an attempt to make an end of thetransmission of the DL PPDU 604 occur at approximately a time at whichthe UL NDP 516-2 from STA2 would have ended if STA2 had transmitted theUL NDP 516-2. In an embodiment, the AP 114 i) chooses the first MCS, andii) adds padding to the data portion of the DL PPDU 604, in an attemptto make an end of the transmission of the DL PPDU 604 occur atapproximately a time at which the UL NDP 516-2 from STA2 would haveended if STA2 had transmitted the UL NDP 516-2. Additionally oralternatively, the AP 114 adjusts a start transmission time of the DLPPDU 604 in an attempt to make an end of the transmission of the DL PPDU604 occur at approximately a time at which the UL NDP 516-2 from STA2would have ended if STA2 had transmitted the UL NDP 516-2, according tosome embodiments.

FIG. 7 is a flow diagram of an example method 700 for performing aranging measurement procedure, according to an embodiment. In someembodiments, the network interface device 122 of FIG. 1 is configured toimplement the method 700. For ease of explanation, the method 700 isdescribed in the context of the network interface device 122implementing the method 700. In other embodiments, however, the method700 is implemented by another suitable communication device.

At block 704, a first communication device prompts (e.g., the networkinterface device 122 prompts) a plurality of second communicationdevices (e.g., client stations 154) to transmit, during a contiguoustime period reserved for a range measurement exchange, respective firstNDPs at respective times. In an embodiment, the contiguous time periodis reserved for an MU ranging measurement exchange. In an embodiment theMU ranging measurement exchange is an exchange of packets between atleast three communication devices (e.g., the first communication deviceand at least two second communication devices).

In an embodiment, the AP 114 selects (e.g., the network interface device122 selects) a set of multiple client stations to transmit NDPssimultaneously such that the receive power of the multiple NPDs at theAP 114 is within a suitable range. The AP 114 prompts client stationscorresponding to significantly different receive power at the AP 114(e.g., not within the suitable range) to transmit NDPs at differenttimes.

In an embodiment, block 704 includes transmitting, by the firstcommunication device, a plurality of packets that include respectivetrigger frames, wherein the packets that include respective triggerframes are transmitted at respective times, and wherein each triggerframe is configured to prompt a respective set of one or more secondcommunication devices to transmit the respective first NDP(s). Forexample, with reference to FIG. 3 , the AP 114 transmits a plurality ofpackets 312, each including a respective trigger frame, wherein eachtrigger frame is configured to prompt a respective set of one or moreclient stations 154 to transmit a respective NDP(s) 316 to the AP 114.

In another embodiment, block 704 includes transmitting, by the firstcommunication device, packets that include respective NDPA frames,wherein the packets that include the respective NDPA frames aretransmitted at respective times, and wherein each NDPA frame isconfigured to: i) announce transmission of a respective second NDP bythe first communication device, and prompt the respective set of one ormore second communication devices to transmit the respective firstNDP(s). For example, with reference to FIG. 4 , the AP 114 transmits aplurality of packets 412, each including a respective NDPA frame,wherein each NDPA frame is configured to prompt a respective set of oneor more client stations 154 to transmit a respective NDP(s) 420 to theAP 114.

In yet another embodiment, block 704 includes transmitting, by the firstcommunication device, a packet with a trigger frame that is configuredto prompt the plurality of second communication devices to transmit therespective first NDPs at respective times. For example, with referenceto FIG. 5 , the AP 114 transmits the packet 512, which includes atrigger frame that is configured to prompt the plurality of clientstations 154 to transmit respective first NDPs 516 at respective times.

At block 708, the first communication device receives (e.g., the networkinterface device 122 receives, the PHY processor 130 receives, etc.)first NDPs from at least some of the second communication devices (e.g.,client stations 154) during the contiguous time period. The first NDPsreceived at block 708 are transmitted by the at least some secondcommunication devices in response to the prompting at block 704.

For example, with reference to FIG. 3 , the AP 114 receives at leastsome of the NDPs 316, according to an embodiment. As another example,with reference to FIG. 4 , the AP 114 receives at least some of the NDPs420, according to another embodiment. As another example, with referenceto FIG. 5 , the AP 114 receives at least some of the NDPs 516, accordingto another embodiment.

In an embodiment in which block 704 includes transmitting a packet witha trigger frame that is configured to prompt the plurality of secondcommunication devices to transmit the respective first NDPs atrespective times, the method 700 further comprises: in response todetermining, at the first communication device (e.g., at the networkinterface device 122, at the MAC processor 126, etc.), that one of thesecond communication devices did not begin transmitting the respectivefirst NDP within a predetermined time period, the first communicationdevice transmits (e.g., the network interface device 122 transmits, thePHY processor 130 transmits, etc.), a further packet with a furthertrigger frame that is configured to prompt one or more remaining secondcommunication devices to transmit, respective first NDPs at respectivetimes.

At block 712, the first communication device transmits (e.g., thenetwork interface device 122 transmits, the PHY processor 130 transmits,etc.) one or more second NDPs to the second communication devices (e.g.,client stations 154) during the contiguous time period.

For example, with reference to FIGS. 3 and 5 , the AP 114 transmits theNDP 236, according to an embodiment. The method 700 further comprisestransmitting (e.g., the first communication device transmits, thenetwork interface device 122 transmits, the PHY processor 130 transmits,etc.) a packet having an NDPA frame (e.g., the packet 228) prior totransmitting the NDP 236, according to an embodiment.

As another example, with reference to FIG. 4 , the AP 114 transmits theNDPs 416, according to an embodiment. The method 700 further comprisestransmitting (e.g., the first communication device transmits, thenetwork interface device 122 transmits, the PHY processor 130 transmits,etc.) a respective packet having an NDPA frame (e.g., the packets 412)prior to transmitting each NDP 416, according to an embodiment.

At block 716, the first communication device uses (e.g., the networkinterface device 122 uses, the MAC processor 126 uses, etc.) receptionof the first NDPs and transmission of the one or more second NDPs todetermine respective ranges between the first communication device andrespective second communication devices. For example, the networkinterface device 122 uses (e.g., the MAC processor 126 uses) i) recordedtimes of reception of the first NDPs, ii) recorded time(s) oftransmission of the second NDP(s), and range measurement feedback fromthe at least some of the second communication devices to determinerespective ranges between the first communication device and the atleast some of the second communication devices, according to anembodiment.

FIG. 8 is a flow diagram of another example method 800 for performing aranging measurement procedure, according to an embodiment. In someembodiments, the network interface device 162 of FIG. 11 is configuredto implement the method 800. For ease of explanation, the method 800 isdescribed in the context of the network interface device 162implementing the method 800. In other embodiments, however, the method800 is implemented by another suitable communication device.

At block 804, a first communication device receives a packet from asecond communication device, the packet including information configuredto prompt the first communication device to transmit a first NDP duringa contiguous time period reserved for a range measurement exchangeinvolving the first communication, the second communication device, andone or more other communication devices. In an embodiment, thecontiguous time period is reserved for an MU ranging measurementexchange. In an embodiment the MU ranging measurement exchange is anexchange of packets between at least three communication devices (e.g.,the first communication, the device, and one or more other communicationdevices).

In an embodiment, the packet received at block 804 i) includes a triggerframe, and ii) is one packet among a plurality of packets that includerespective trigger frames; the packets that include respective triggerframes are transmitted by the second communication device at respectivetimes; each trigger frame is configured to prompt a respective set ofone or more communication devices in a group of communication devices totransmit a respective NDP(s); and the group includes the firstcommunication device and the one or more other communication devices.For example, with reference to FIG. 3 , the AP 114 transmits a pluralityof packets 312, each including a respective trigger frame, wherein eachtrigger frame is configured to prompt a respective set of one or moreclient stations 154 to transmit a respective NDP(s) 316 to the AP 114.

In another embodiment, the packet received at block 804 i) includes anNDPA frame, and ii) is one packet among a plurality of packets thatinclude respective NDPA frames; the packets that include respective NDPAframes are transmitted by the second communication device at respectivetimes; each null data packet announcement frame is configured to:announce transmission of a respective second NDP by the secondcommunication device, and prompt a respective set of one or morecommunication devices in the group of communication devices to transmita respective NDP(s); and the group includes the first communicationdevice and the one or more other communication devices.

For example, with reference to FIG. 4 , the AP 114 transmits a pluralityof packets 412, each including a respective NDPA frame, wherein eachNDPA frame is configured to prompt a respective set of one or moreclient stations 154 to transmit a respective NDP(s) 420 to the AP 114.

In yet another embodiment, the packet received at block 804 includes atrigger frame that is configured to: i) prompt the first communicationdevice (and one or more other first communication devices) to transmitthe first NDP (simultaneously while the one or more other firstcommunication devices transmit NDPs), and ii) prompt one or more othersecond communication devices to transmit the respective other NDPs atone or more other respective times. For example, with reference to FIG.5 , the AP 114 transmits the packet 512, which includes a trigger framethat is configured to prompt the plurality of client stations 154 totransmit respective first NDPs 516 at respective times.

In an embodiment in which block 804 includes receiving a packet with atrigger frame that is configured to i) prompt the first communicationdevice to transmit the first NDP, and ii) prompt the one or more othersecond communication devices to transmit the respective other NDPs atone or more other respective times, the method 800 further comprises:receiving, at the first communication device, a further packet with afurther trigger frame that is configured to prompt the firstcommunication device to transmit the first NDP; wherein the furtherpacket is received during a time period in which one of the other secondcommunication devices was expected to transmit another NDP to the secondcommunication device.

At block 808, the first communication device transmits (e.g., thenetwork interface device 162 transmits, the PHY processor 170 transmits,etc.) the first NDP to the second communication device during thecontiguous time period. In an embodiment, the first communication devicetransmits the first NDP in response to receiving the packet at block804. In another embodiment, the first communication device transmits thefirst NDP in response to receiving the further packet with the furthertrigger frame.

For example, with reference to FIG. 3 , STA3 transmits the NDP 316-3 inresponse to receiving the packet 312-3, according to an embodiment, Asanother example, with reference to FIG. 4 , STA3 transmits the NDP 420-3in response to receiving the packet 412-3, according to anotherembodiment. As another example, with reference to FIG. 5 , STA3transmits the NDP 516-3 in response to receiving the packet 512,according to another embodiment. As another example, with reference toFIG. 6 , STA3 transmits the NDP 516-3 in response to receiving thepacket 604, according to another embodiment.

At block 812, the first communication device receives (e.g., the networkinterface device 162 receives, the PHY processor 170 receives, etc.) asecond NDP from the second communication device (e.g., the AP 114)during the contiguous time period.

For example, with reference to FIGS. 3 and 5 , STA3 receives the NDP236, according to an embodiment. The method 800 further comprisesreceiving (e.g., the first communication device receives, the networkinterface device 162 receives, the PHY processor 170 receives, etc.) apacket having an NDPA frame (e.g., the packet 228) prior to receivingthe NDP 236, according to an embodiment.

As another example, with reference to FIG. 4 , STA3 receives NDP 416-3,according to an embodiment. The method 800 further comprises receiving(e.g., the first communication device receives, the network interfacedevice 162 receives, the PHY processor 170 receives, etc.) the packet412-3 prior to receiving the NDP 416-3, according to an embodiment.

At block 816, the first communication device uses (e.g., the networkinterface device 162 uses, the MAC processor 166 uses, etc.)transmission of the first NDP and reception of the second NDP todetermine a range between the first communication device and the secondcommunication device. For example, the network interface device 162 uses(e.g., the MAC processor 166 uses) i) a recorded time of transmission ofthe first NDP, ii) a recorded time of reception of the second NDP, andrange measurement feedback from the second communication device todetermine a range between the first communication device and the secondcommunication device, according to an embodiment.

In another embodiment, block 816 is omitted, and the method furtherincludes transmitting, by the first communication device (e.g., thenetwork interface device 162 transmits, the PHY processor 170 transmits,etc.) range measurement feedback to the second communication device sothat the second communication device can determine the range between thefirst communication device and the second communication device. In anembodiment, in which the method further includes transmitting, by thefirst communication device, the range measurement feedback to the secondcommunication device, block 816 is omitted.

Embodiment 1: A method for performing a ranging measurement procedure,the method comprising: prompting, at a first communication device, aplurality of second communication devices to transmit, during acontiguous time period reserved for a range measurement exchange,respective first null data packets (NDPs) at respective times;receiving, at the first communication device, first NDPs from at leastsome of the second communication devices during the contiguous timeperiod; transmitting, by the first communication device, one or moresecond NDPs to the plurality of second communication devices; and using,at the first communication device, reception of the first NDPs andtransmission of the one or more second NDPs to determine respectiveranges between the first communication device and respective secondcommunication devices.

Embodiment 2: The method of Embodiment 1, wherein prompting theplurality of second communication devices to transmit the respectivefirst NDPs comprises: transmitting, by the first communication device, aplurality of packets that include respective trigger frames, wherein thepackets that include respective trigger frames are transmitted atrespective times, and wherein each trigger frame is configured to prompta respective set of one or more second communication devices to transmitone or more respective first NDPs.

Embodiment 3: The method of Embodiment 1, wherein prompting theplurality of second communication devices to transmit the respectivefirst NDPs comprises: transmitting, by the first communication device,packets that include respective null data packet announcement frames,wherein the packets that include respective null data packetannouncement frames are transmitted at respective times, and whereineach null data packet announcement frame is configured to: announcetransmission of a respective second NDP by the first communicationdevice, and prompt a respective set of one or more second communicationdevices to transmit a respective set of one or more first NDPs; whereintransmitting the one or more second NDPs to the plurality of secondcommunication devices comprises transmitting a respective second NDPafter transmission of each packet that includes the respective null datapacket announcement frame.

Embodiment 4: The method of Embodiment 1, wherein prompting theplurality of second communication devices to transmit the respectivefirst NDPs comprises: transmitting, by the first communication device, apacket with a trigger frame that is configured to prompt the pluralityof second communication devices to transmit the respective first NDPs atrespective times.

Embodiment 5: The method of Embodiment 4, further comprising: inresponse to determining, at the first communication device, that one ofthe second communication devices did not begin transmitting therespective first NDP within a predetermined time period, transmitting,by the first communication device, a further packet with a furthertrigger frame that is configured to prompt one or more remaining secondcommunication devices to transmit respective first NDPs at respectivetimes.

Embodiment 6: An apparatus, comprising: a network interface deviceassociated with a first communication device, wherein the networkinterface device is implemented on one or more integrated circuit (IC)devices, and wherein the network interface device is configured to:prompt a plurality of second communication devices to transmit, during acontiguous time period reserved for a range measurement exchange,respective first null data packets (NDPs) at respective times, receivefirst NDPs from at least some of the second communication devices duringthe contiguous time period, transmit one or more second NDPs to theplurality of second communication devices, and use reception of thefirst NDPs and transmission of the one or more second NDPs to determinerespective ranges between the first communication device and respectivesecond communication devices.

Embodiment 7: The apparatus of Embodiment 6, wherein the networkinterface device is configured to: transmit a plurality of packets thatinclude respective trigger frames, wherein the packets that includerespective trigger frames are transmitted at respective times, andwherein each trigger frame is configured to prompt a respective set ofone or more second communication devices to transmit one or morerespective first NDPs.

Embodiment 8: The apparatus of Embodiment 6, wherein the networkinterface device is configured to: transmit packets that includerespective null data packet announcement (NDPA) frames, wherein thepackets that include respective NDPA frames are transmitted atrespective times, and wherein each NDPA frame is configured to: announcetransmission of a respective second NDP by the first communicationdevice, and prompt a respective set of one or more second communicationdevices to transmit a respective set of one or more first NDPs. Thenetwork interface device is configured to: transmit a respective secondNDP after transmission of each packet that includes the respective NDPAframe.

Embodiment 9: The apparatus of Embodiment 6, wherein the networkinterface device is configured to: transmit a packet with a triggerframe that is configured to prompt the plurality of second communicationdevices to transmit the respective first NDPs at respective times.

Embodiment 10: The apparatus of Embodiment 9, wherein the networkinterface device is configured to: in response to determining, at thenetwork interface device, that one of the second communication devicesdid not begin transmitting the respective first NDP within apredetermined time period, transmit a further packet with a furthertrigger frame that is configured to prompt one or more remaining secondcommunication devices to transmit respective first NDPs at respectivetimes.

Embodiment 11: A method for performing a ranging measurement procedure,the method comprising: receiving, at a first communication device, apacket from a second communication device, the packet includinginformation configured to prompt the first communication device totransmit a first null data packet (NDP) during a contiguous time periodreserved for a range measurement exchange involving the firstcommunication, the second communication device, and one or more othercommunication devices; responsive to receiving the packet, transmitting,by the first communication device, the first NDP to the secondcommunication device during the contiguous time period; receiving, bythe first communication device, a second NDP from the secondcommunication during the contiguous time period; and using, at the firstcommunication device, transmission of the first NDP and reception of thesecond NDP to determine a range between the first communication deviceand the second communication device.

Embodiment 12: The method of Embodiment 11, wherein: the packet thatincludes the information configured to prompt the first communicationdevice to transmit the first NDP during the contiguous time period i)includes a trigger frame, and ii) is one packet among a plurality ofpackets that include respective trigger frames; the packets that includerespective trigger frames are transmitted by the second communicationdevice at respective times; each trigger frame is configured to prompt arespective set of one or more communication devices in a group ofcommunication devices to transmit a respective set of one or more NDPs;and the group includes the first communication device and the one ormore other communication devices.

Embodiment 13: The method of Embodiment 11, wherein: the packet thatincludes the information configured to prompt the first communicationdevice to transmit the first NDP during the contiguous time period i)includes a null data packet announcement (NDPA) frame, and ii) is onepacket among a plurality of packets that include respective NDPA frames;the packets that include respective NDPA frames are transmitted by thesecond communication device at respective times; each null data packetannouncement frame is configured to: announce transmission of arespective second NDP by the second communication device, and prompt arespective set of one or more communication devices in a group ofcommunication devices to transmit a respective set of one or more NDPs;the group includes the first communication device and the one or moreother communication devices; and the first communication device receivesthe second NDP from the second communication after receiving the onepacket that includes the NDPA frame,

Embodiment 14: The method of Embodiment 11, wherein: the packet thatincludes information configured to prompt the first communication deviceto transmit the first NDP includes a trigger frame that is configuredto: i) prompt the first communication device to transmit the first NDP,and ii) prompt at least some of the one or more communication devices totransmit respective other NDPs at one or more other respective times.

Embodiment 15: The method of Embodiment 14, further comprising:receiving, at the first communication device, a further packet with afurther trigger frame that is configured to prompt the firstcommunication device to transmit the first NDP; wherein the furtherpacket is received during a time period in which one of the othercommunication devices was expected to transmit another NDP to the secondcommunication device.

Embodiment 16: An apparatus, comprising: a network interface deviceassociated with a first communication device, wherein the networkinterface device is implemented on one or more integrated circuit (IC)devices, and wherein the network interface device is configured to:receive a packet from a second communication device, the packetincluding information configured to prompt the first communicationdevice to transmit a first null data packet (NDP) during a contiguoustime period reserved for a range measurement exchange involving thefirst communication, the second communication device, and one or moreother communication devices, responsive to receiving the packet,transmits the first NDP to the second communication device during thecontiguous time period, receive a second NDP from the secondcommunication during the contiguous time period, and use transmission ofthe first NDP and reception of the second NDP to determine a rangebetween the first communication device and the second communicationdevice.

Embodiment 17: The apparatus of Embodiment 16, wherein: the packet thatincludes the information configured to prompt the first communicationdevice to transmit the first NDP during the contiguous time period i)includes a trigger frame, and ii) is one packet among a plurality ofpackets that include respective trigger frames; the packets that includerespective trigger frames are transmitted by the second communicationdevice at respective times; each trigger frame is configured to prompt arespective set of one or more communication devices in a group ofcommunication devices to transmit a respective set of one or more NDPs;and the group includes the first communication device and the one ormore other communication devices.

Embodiment 18: The apparatus of Embodiment 16, wherein: the packet thatincludes the information configured to prompt the first communicationdevice to transmit the first NDP during the contiguous time period i)includes a null data packet announcement (NDPA) frame, and ii) is onepacket among a plurality of packets that include respective NDPA frames;the packets that include respective NDPA frames are transmitted by thesecond communication device at respective times; each null data packetannouncement frame is configured to: announce transmission of arespective second NDP by the second communication device, and prompt arespective set of one or more communication devices in a group ofcommunication devices to transmit a respective set of one or more NDPs;the group includes the first communication device and the one or moreother communication devices; and the first communication device receivesthe second NDP from the second communication after receiving the onepacket that includes the NDPA frame.

Embodiment 19: The Embodiment of claim 16, wherein: the packet thatincludes information configured to prompt the first communication deviceto transmit the first NDP includes a trigger frame that is configuredto: i) prompt the first communication device to transmit the first NDP,and ii) prompt at least some of the one or more communication devices totransmit respective other NDPs at one or more other respective times.

Embodiment 20: The apparatus of Embodiment 16, wherein: the networkinterface device is configured to receive a further packet with afurther trigger frame that is configured to prompt the firstcommunication device to transmit the first NDP; and wherein the furtherpacket is received during a time period in which one of the othercommunication devices was expected to transmit other NDP to the secondcommunication device.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. The software or firmware instructions mayinclude machine readable instructions that, when executed by one or moreprocessors, cause the one or more processors to perform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for performing a ranging measurementprocedure, the method comprising: determining, by a first communicationdevice, a plurality of second communication devices from a plurality ofthird communication devices to transmit first null data packets (NDPs);prompting, at a first communication device, the selected plurality ofsecond communication devices to transmit, during a contiguous timeperiod reserved for a range measurement exchange, the respective firstNDPs at respective times, wherein remaining communication devices of theplurality of third communications are not prompted to transmit duringthe contiguous time period the first NDPs; receiving, at the firstcommunication device, the first NDPs from at least some of the selectedsecond communication devices during the contiguous time period, whereinthe first NDPs are received at a respective receive power within thereceive power range; transmitting, by the first communication device,one or more second NDPs to the selected plurality of secondcommunication devices; and using, at the first communication device,reception of the first NDPs to determine respective ranges between thefirst communication device and respective selected second communicationdevices.
 2. The method of claim 1 wherein the using includes using thetransmission of the one or more second NDPs to determine respectiveranges between the first communication device and respective selectedsecond communication devices.
 3. The method of claim 1, whereinprompting the selected plurality of second communication devices totransmit the respective first NDPs comprises: transmitting, by the firstcommunication device, a plurality of packets that include respectivetrigger frames, wherein the packets that include respective triggerframes are transmitted at respective times, and wherein each triggerframe is configured to prompt a respective set of one or more secondcommunication devices to transmit one or more respective first NDPs. 4.The method of claim 1, wherein prompting the selected plurality ofsecond communication devices to transmit the respective first NDPscomprises: transmitting, by the first communication device, packets thatinclude respective null data packet announcement frames, wherein thepackets that include respective null data packet announcement frames aretransmitted at respective times, and wherein each null data packetannouncement frame is configured to: announce transmission of arespective second NDP by the first communication device, and prompt arespective set of one or more second communication devices to transmit arespective set of one or more first NDPs; wherein transmitting the oneor more second NDPs to the selected plurality of second communicationdevices comprises transmitting a respective second NDP aftertransmission of each packet that includes the respective null datapacket announcement frame.
 5. The method of claim 1, wherein promptingthe selected plurality of second communication devices to transmit therespective first NDPs comprises: transmitting, by the firstcommunication device, a packet with a trigger frame that is configuredto prompt the selected plurality of second communication devices totransmit the respective first NDPs at respective times.
 6. The method ofclaim 5, further comprising: in response to determining, at the firstcommunication device, that one of the selected second communicationdevices did not begin transmitting the respective first NDP within apredetermined time period, transmitting, by the first communicationdevice, a further packet with a further trigger frame that is configuredto prompt one or more remaining selected second communication devices totransmit respective first NDPs at respective times.
 7. An apparatus,comprising: a network interface device associated with a firstcommunication device, wherein the network interface device isimplemented on one or more integrated circuit (IC) devices, and whereinthe network interface device is configured to: determine, by a firstcommunication device, a plurality of second communication devices from aplurality of third communication devices to transmit first null datapackets (NDPs); prompt a plurality of the selected second communicationdevices to transmit, during a contiguous time period reserved for arange measurement exchange, respective first NDPs at respective times,wherein remaining communication devices of the plurality of thirdcommunications are not prompted to transmit the first NDPs during thecontiguous time period; receive the first NDPs from at least some of theselected second communication devices during the contiguous time period,wherein the first NDPs are received at the respective receive powerwithin the receive power range; transmit one or more second NDPs to theselected plurality of second communication devices, and use reception ofthe first NDPs and transmission of the one or more second NDPs todetermine respective ranges between the first communication device andrespective selected second communication devices.
 8. The apparatus ofclaim 7 wherein the network interface device is configured to usetransmission of the one or more second NDPs to determine respectiveranges between the first communication device and respective selectedsecond communication devices.
 9. The apparatus of claim 7, wherein thenetwork interface device is configured to: transmit a plurality ofpackets that include respective trigger frames, wherein the packets thatinclude respective trigger frames are transmitted at respective times,and wherein each trigger frame is configured to prompt a respective setof one or more selected second communication devices to transmit one ormore respective first NDPs.
 10. The apparatus of claim 7, wherein thenetwork interface device is configured to: transmit packets that includerespective null data packet announcement (NDPA) frames, wherein thepackets that include respective NDPA frames are transmitted atrespective times, and wherein each NDPA frame is configured to: announcetransmission of a respective second NDP by the first communicationdevice, and prompt a respective set of one or more selected secondcommunication devices to transmit a respective set of one or more firstNDPs; transmit a respective second NDP after transmission of each packetthat includes the respective NDPA frame.
 11. The apparatus of claim 7,wherein the network interface device is configured to: transmit a packetwith a trigger frame that is configured to prompt the selected pluralityof second communication devices to transmit the respective first NDPs atrespective times.
 12. The apparatus of claim 11, wherein the networkinterface device is configured to: in response to determining, at thenetwork interface device, that one of the second communication devicesdid not begin transmitting the respective first NDP within apredetermined time period, transmit a further packet with a furthertrigger frame that is configured to prompt one or more remainingselected second communication devices to transmit respective first NDPsat respective times.
 13. A method for performing a ranging measurementprocedure, the method comprising: receiving, at a first communicationdevice, a packet from a second communication device, the packetincluding information configured to prompt the first communicationdevice to transmit a first null data packet (NDP) during a contiguoustime period reserved for a range measurement exchange involving thefirst communication, the second communication device, and one or moreother communication devices, wherein the first communication device andthe one or more other communication devices are determined from a thirdplurality of communication devices by the second communication device,wherein the contiguous time period reserved for the range measurementexchange does not involve the remaining communication devices of theplurality of third communication devices; responsive to receiving thepacket, transmitting, by the first communication device, the first NDPto the second communication device during the contiguous time periodsuch that the first NDP will be received by the second communicationdevice within a receive power range; receiving, by the firstcommunication device, a second NDP from the second communication deviceduring the contiguous time period; and wherein the transmission of thefirst NDP and reception of the second NDP are used to determine a rangebetween the first communication device and the second communicationdevice.
 14. The method of claim 13, wherein: the packet that includesthe information configured to prompt the first communication device totransmit the first NDP during the contiguous time period i) includes atrigger frame, and ii) is one packet among a plurality of packets thatinclude respective trigger frames; the packets that include respectivetrigger frames are transmitted by the second communication device atrespective times; each trigger frame is configured to prompt arespective set of one or more communication devices in a group ofcommunication devices to transmit a respective set of one or more NDPs;and the group includes the first communication device and the one ormore other communication devices.
 15. The method of claim 13, wherein:the packet that includes the information configured to prompt the firstcommunication device to transmit the first NDP during the contiguoustime period i) includes a null data packet announcement (NDPA) frame,and ii) is one packet among a plurality of packets that includerespective NDPA frames; the packets that include respective NDPA framesare transmitted by the second communication device at respective times;each null data packet announcement frame is configured to: announcetransmission of a respective second NDP by the second communicationdevice, and prompt a respective set of one or more communication devicesin a group of communication devices to transmit a respective set of oneor more NDPs; the group includes the first communication device and theone or more other communication devices; and the first communicationdevice receives the second NDP from the second communication afterreceiving the one packet that includes the NDPA frame.
 16. The method ofclaim 13, wherein: the packet that includes information configured toprompt the first communication device to transmit the first NDP includesa trigger frame that is configured to: i) prompt the first communicationdevice to transmit the first NDP, and ii) prompt at least some of theone or more communication devices to transmit respective other NDPs atone or more other respective times.
 17. The method of claim 16, furthercomprising: receiving, at the first communication device, a furtherpacket with a further trigger frame that is configured to prompt thefirst communication device to transmit the first NDP; wherein thefurther packet is received during a time period in which one of theother communication devices was expected to transmit another NDP to thesecond communication device.